The well-known difficulty in distinguishing the response to a combination headache medication and its individual components in the presence of a high placebo response was again demonstrated in a randomized, double-blind, placebo-controlled, multi-center trial comparing Fiorinal with Codeine and its Fiorinal and codeine phosphate components in relieving the pain, tension, and muscle contraction associated with tension headache. In the original analysis of the study data, no distinction was apparent between patient response to Fiorinal with Codeine and the response to the individual components, a finding that appeared to conflict with the results of a similar earlier study. This apparent discrepancy was attributable to a high placebo response in the later study. Separation of study subjects according to their baseline level of anxiety and pain identified a subset of less anxious patients with mild to moderate pain severity who were least likely to respond to placebo. Analysis of data from these patients showed that Fiorinal with Codeine was significantly better than placebo in improving patients' self-ratings of various symptoms of tension headache at 0.5, 1, 2, 3, and 4 hours after ingestion of the study medication. The combination drug was also consistently superior to Fiorinal alone and codeine alone in improving the patients' self-evaluation items, and differences between the combination and its components were generally of statistical or borderline significance during the last half of the study. The investigators' assessments of the effect of treatment on the three principal variables in tension headache (namely, headache pain, psychic tension, and muscle contraction of the head, neck, and shoulders) at the final patient visit also showed Fiorinal with Codeine to be not only significantly superior to placebo but also consistently superior to either component. The superiority of the combination over Fiorinal alone achieved borderline significance for headache pain and psychic tension.